1. Field of the Invention
The invention relates to electro-optic system test equipment and, more specifically, to test equipment for measuring the boresight alignment of electro-optic systems having a line-of-sight sensor for detecting and locating a target and a line-of-sight illumination device for illuminating or designating the target.
2. Description of the Related Art
Recent improvements in military and commercial electro-optic ("E-O") systems have been made by incorporating two or more major functions into a single piece of equipment. For example, a military E-O system might incorporate a line-of-sight sensor subsystem such as a forward looking infrared sensor ("FLIR") for detecting and locating a target in darkness, and a line-of-sight illumination subsystem such as a laser designator for illuminating or designating the target.
The FLIR is a passive device capable of identifying the location of a target in its line-of-sight viewing aperture based on the infrared signature of the target. For convenience here, the FLIR is assumed to have a target vector which the FLIR directs to the target. The target vector is an imaginary line (a mathematical construction) extending from the center of the FLIR aperture to the center of the target signature (centroid of the signature beam) which is used to represent the physical geometric location of the target relative to the FLIR.
The laser designator is an active device that generates and projects a laser illumination beam onto the target identified by the FLIR, where laser illumination beam as used herein is not restricted to a particular band of wavelengths. The direction of the illumination beam is defined by an imaginary line extending from the center of the laser designator's output aperture and running along the centroid of the beam. The laser designator includes a steering mechanism for steering the illumination beam to the target and maintaining the beam on the target during movements of the target relative to the E-O system.
The relative mounting positions of the FLIR and laser designator on the E-O system are usually offset. This offset can be effectively eliminated and the target vector and illumination beam can be made concentric, for example, by placing a beam-splitter at or near the FLIR aperture and directing the illumination beam to the beamsplitter with a mirror. For E-O system designs in which the FLIR and laser designator offset is maintained, this offset is typically sufficiently small relative to the target range that the target vector and the illumination beam can be assumed to be coincident, as may the FLIR and laser designator apertures. The boresight alignment of the E-O system as that term is used here refers to this line of coincidence between the target vector and the illumination beam expressed in angular terms.
The angular alignment of the FLIR target vector and the illumination beam is referred to here as boresight alignment. Boresight alignment is essential for proper operation of multispectral E-O systems as described above, regardless of their specific design, since the laser designator will accurately illuminate the target located by the FLIR only if the E-O system is properly boresight aligned.
The FLIR and laser designator, however, typically operate on different physical principles, most often in different bands or regions of the electromagnetic spectrum. Typical FLIR night vision systems cover the 8- to 12-micron (micrometer) wavelength band, while typical laser target designators radiate at about one micron. Techniques, designs and materials used to manipulate radiation in these different bands can differ significantly. These factors have led to difficulty in designing equipment to test the boresight alignment of such E-O systems.
In the past, boresight alignment was typically monitored and maintained by measuring the FLIR target vector and the position of the laser illumination beam with respect to a common physical or structural component of the E-O system or its supporting platform. The location of the component provided a common reference point from which the positions of the target vector and illumination beam could be independently measured and then compared. This design approach was generally unsatisfactory in practice since it was difficult to maintain necessary physical tolerances throughout system manufacture and during operation. For example, operational conditions for such systems typically include error-inducing motion and structural vibrations as well as environmental effects such as large variations in temperature, pressure and humidity.
One example of a known system for measuring FLIR-to-laser boresight alignment provides a replaceable film target through which the laser designator burns a hole. The FLIR is then focused on the film while the hole is back-lighted with long-wavelength radiation detectable by the FLIR. This design has a number of drawbacks. For example, its accuracy is not only a direct function of FLIR-to-laser alignment, but also of the dimensions of the burned hole and the operational characteristics of the laser designator. Furthermore, the equipment is only suitable for static testing since it is large, bulky and susceptible to motion.
Another example of a known FLIR-to-laser boresight alignment tester is specifically classed as an "operational level" flight line tester and was designed to test the E-O system, including its FLIR-to-laser boresight alignment, of a particular aircraft. The E-O system of the aircraft includes FLIR sensor and laser designator subsystems having apertures which are offset from one another. Aperture dimensions and center-to-center spacing between apertures are fixed. The tester has separate optical collimators for testing each subsystem, and separate emitters and detectors to accomplish various tests with each collimator. Among the detectors is a quadrature laser detector to establish FLIR-to-laser boresight. This tester measures boresight alignment while accomodating the FLIR-to-laser offset.
This tester design also has a number of drawbacks due largely to its specific applicability to a particular aircraft. For example, the alignment of the quadrature laser detector to the FLIR test collimator boresight must be set in the factory, and any variation of alignment due to tester handling or aging requires realignment at the factory or depot. In addition, the tester must be firmly attached to the E-O system under test and cannot accommodate relative motion between the E-O system and the tester.
Other known E-O system boresight alignment test equipment designs include a family of testers designed and developed by the assignee of the present invention. An example of this family of testers is disclosed in U.S. Pat. No. 4,626,685, which provides a multispectral collimator having reflective diamond-machined optical elements for producing a target signature, and refractive or reflective optical elements for directing the laser beam of a laser designator to one or more detector elements.
Although this design provided a number of improvements and advantages over other known systems, it also was designed for static operation and allowed no relative movement between tester and the E-O system under test.
Accordingly, it is an object of the invention to provide an apparatus and method for static and dynamic testing of the boresight alignment of an E-O system.
It is also an object of the invention to provide an apparatus and method for static and dynamic testing the boresight alignment of an E-O system which do not require a common physical reference point on the E-O system.
It is further an object of the invention to provide an apparatus and method for static and dynamic testing the boresight alignment of an E-O system which operate independently of laser designator operational characteristics other than pointing.
It is still further an object of the invention to provide an apparatus and method for static and dynamic testing the boresight alignment of an E-O system which are adaptable to a wide range of E-O system designs.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.